At present there are many known and widely-used techniques for heating a food product, both for thawing and for cooking.
According to some known heating techniques, the food product receives heat through its outer surface, which exchanges heat with an external heating element or with an external environment which is at a higher temperature. In these techniques, the flow of heat inside the food product is determined by the temperature gradient and by thermal diffusivity of the food product itself.
According to other known heating techniques, heat is generated directly inside the food product by means of electromagnetic fields or electromagnetic radiations. Amongst these, some techniques use radio frequency (RF) dielectric heating and other techniques use microwaves (MW). Conventionally, radio frequency electromagnetic waves lie within the band of frequencies between 1 and 300 MHz, whilst microwaves lie within the band of frequencies between 300 MHz and 300 GHz. In particular, radio frequency heating devices and microwave heating devices are known and widely utilized.
Electromagnetic heating techniques that use radio frequency or microwaves are generally useful for achieving shorter thawing or cooking times than techniques that use heat exchange through the surface of the food product. However, a problem common to many known electromagnetic heating techniques relates to the difficulty of obtaining a sufficiently homogeneous distribution of the temperature inside the food product.
Moreover, another problem of known electromagnetic heating techniques is encountered when several identical loads (or portions) of a food product are simultaneously heated. In these cases, it often occurs that the temperatures of the loads are not similar to each other at the end of the heating procedure, i.e., it is not possible to obtain an acceptable spatial uniformity of heating.
These problems normally seem to be more significant for microwave heating devices.
Therefore, it would be desirable to have available a heating technique, in particular using microwaves, which enables a reduction in the non-uniformity of temperature distribution in the food product and/or among loads of food product during heating thereof.